linux-kernel - Re: [RESEND][PATCHv2 1/3] ion: Devicetree bindings for Ion

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Date:	Mon, 11 Jan 2016 17:28:23 -0600
From:	Rob Herring <robh+dt@...nel.org>
To:	Laura Abbott <laura@...bott.name>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Andrew Andrianov <andrew@...mnt.org>, arve@...roid.com,
	Riley Andrews <riandrews@...roid.com>,
	John Stultz <john.stultz@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tom Gall <tom.gall@...aro.org>,
	Colin Cross <ccross@...gle.com>, devel@...verdev.osuosl.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rom Lemarchand <romlem@...gle.com>,
	Mitchel Humpherys <mitchelh@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Feng Tang <feng.tang@...el.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [RESEND][PATCHv2 1/3] ion: Devicetree bindings for Ion

On Mon, Jan 11, 2016 at 3:39 PM, Laura Abbott <laura@...bott.name> wrote:
>
> This adds a base set of devicetree bindings for the Ion memory
> manager. This supports setting up the generic set of heaps and
> their properties.
>
> Signed-off-by: Laura Abbott <laura@...bott.name>
> ---
>  drivers/staging/android/ion/devicetree.txt | 50 ++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>  create mode 100644 drivers/staging/android/ion/devicetree.txt
>
> diff --git a/drivers/staging/android/ion/devicetree.txt b/drivers/staging/android/ion/devicetree.txt
> new file mode 100644
> index 0000000..e1ea537
> --- /dev/null
> +++ b/drivers/staging/android/ion/devicetree.txt
> @@ -0,0 +1,50 @@
> +Ion Memory Manager
> +
> +Ion is a memory manager that allows for sharing of buffers via dma-buf.
> +Ion allows for different types of allocation via an abstraction called
> +a 'heap'. A heap represents a specific type of memory. Each heap has
> +a different type. There can be multiple instances of the same heap
> +type.
> +
> +Required properties for Ion
> +
> +- compatible: "linux,ion" PLUS a compatible property for the device
> +
> +All child nodes of a linux,ion node are interpreted as heaps
> +
> +required properties for heaps
> +
> +- compatible: compatible string for a heap type PLUS a compatible property
> +for the specific instance of the heap. Current heap types
> +-- linux,ion-heap-system
> +-- linux,ion-heap-system-contig
> +-- linux,ion-heap-carveout
> +-- linux,ion-heap-chunk
> +-- linux,ion-heap-dma
> +-- linux,ion-heap-custom
> +
> +Optional properties
> +- memory-region: A phandle to a memory region. Required for DMA heap type
> +(see reserved-memory.txt for details on the reservation)

Why would all of them not require a memory region other than system heap?

> +
> +Example:
> +
> +       ion {
> +               compatbile = "qcom,msm8916-ion", "linux,ion";
> +               #address-cells = <1>;
> +               #size-cells = <0>;
> +
> +               ion-system-heap {
> +                       compatbile = "qcom,system-heap", "linux,ion-heap-system"
> +               };

What is the purpose of this in DT? Don't we always want/need a system
heap? How does it vary by platform?

> +               ion-camera-region {
> +                       compatible = "qcom,camera-heap", "linux,ion-heap-dma"
> +                       memory-region = <&camera_region>;

Why not just add a property (or properties) to the camera_region node
that ION drivers can search for?

Rob